1. Field of the Invention (Technical Field)
The present invention relates to methods of disposal and isolation of hazardous wastes, particularly radionuclides.
2. Description of Related Art
One of the great concerns in nuclear energy development throughout the world is the safe disposal and isolation of spent fuels from reactors or waste streams from reprocessing plants. In particular, entrapment of highly volatile radionuclides such as iodine (129I) produced from a fission process and subsequent immobilization of these radionuclides in an appropriate waste form is a great technical challenge because of the high mobility of these radionuclides and the difficulty of incorporating them into any existing waste forms such as glass, ceramics, and grout. Furthermore, a majority (>99%) of 129I will enter into the dissolver off-gas stream during fuel reprocessing. It is thus desirable to develop a material that can effectively entrap gaseous iodine during the off-gas treatment, which then can be directly converted into a durable waste form.
The present invention provides a new concept of applying nanomaterial and nanotechnology to radioactive waste treatment, especially, a method for converting the radioactive nuclide-loaded mesoporous material into a glass-ceramic waste form that can be used either for interim storage or long-term disposal. The invention first fixes iodine inside the nanopores of a getter material by converting molecular iodine into less volatile ionic species. It then vitrifies the nuclides-loaded getter material with additional glass-forming components or commercially available glass frits (e.g., those from Ferro Co.). Preferred compositions and vitrification temperatures (850 to 950° C.) have been established in terms of the durability of the resulting waste form. This has been accomplished by studying various material combinations, the routes for iodine fixation, and different vitrification temperatures. FTIR, EDXRF, high temperature XRD (HTXRD), TEM, XPS, and TGA/DTA have been employed to characterize nuclide behaviors and material structures. It has been found that the formation of nanometer crystalline phases is responsible for iodine immobilization and retention during vitrification and waste form leaching. This is consistent with the determined optimal vitrification temperatures, which are lower than conventional glass-forming temperatures.